The present disclosure relates generally to ballistic containment structures, and more particularly to a sandwich panel with a variable stiffness response for use in ballistic containment systems.
Structures designed for dealing with ballistic events, such as a blade out event for a fan case or the forward bearing support structure of a gas turbine engine, are typically constrained by the mechanical properties of the materials used in the structures. In a blade out event, one or more fan blades or portions thereof in a turbine engine are released, for example, as a result of the ingestion of a foreign object (e.g., a bird). In such an event, the released fan blade must be contained so as not to penetrate the fan case. In addition, after a blade out event the fan case must retain its structural integrity while the engine shuts down in order to prevent further potentially catastrophic damage. Despite these significant ballistic requirements on the fan case, the fan case is a large structure which contributes significantly to the overall weight and drag of the engine. Among the many challenges faced by a person of skill in the art is how to balance the ballistic requirements of the fan case with the competing weight and size constraints. Thus, a high strength fan containment case is of value.